It is highly plausible that heritable individual differences in executive functions (EFs), mediated by variation in identifiable neural circuits, contribute to a generalized genetic vulnerability to psychopathology and psychiatric disorder. Determining the extent to which functional variation in neural circuits supporting EF is itself heritable, or influenced by environmental factors, will provide information critical to understanding the role of neural circuits in mediating the genetic and environmental vulnerability to mental illness. In this competitive renewal, we propose to extend our twin study of individual differences in EFs by conducting the following: (1) the first large-scale functional magnetic resonance imaging (fMRI) study of individual differences in the multiple EFs; (2) the first fMRI study of EFs to incorporate latent variables measured outside of the scanner; and (3) the first behavior genetic study of functional neural indices of these multiple EFs in adulthood. By collecting fMRI data on a carefully selected set of EF tasks and analyzing it in conjunction with additional EF tasks measured outside the scanner, as well as new assessments of psychopathology linked to EFs, we will be able to determine neural circuits related to individual differences in EFs and associated psychopathology. Because the data come from twins, we will also assess the genetic and environmental etiologies of individual differences in these neural indices, and examine their genetic and environmental correlations with the behavioral EF measures. Finally, by integrating the neural data with assessments of symptoms related to psychopathology (e.g., attention problems, depression), we will test whether the brain areas related to EFs mediate the relations between EFs and these symptoms identified in this sample. To achieve these aims we conduct an fMRI study on twins who have participated in the Colorado Longitudinal Twin Study (LTS) since infancy and have previous EF assessments. Based on recruitment rates for prior waves and a pilot study, we estimate 640 participants from 320 twin pairs (167 monozygotic and 153 dizygotic). In the scanner they will perform 3 tasks tapping 3 separable but correlated EFs: inhibiting prepotent responses, updating working memory, and shifting between tasks or mental sets. They will complete 3 additional EF tasks outside the scanner so we can construct latent variables for each component. They will also complete phone interviews and online questionnaire assessments of symptoms related to mental illness before the imaging session. We will analyze the imaging data using independent components analysis to identify separable neural circuits that correlate with individual differences in performance. We will then examine whether these neural measures mediate the relations between EFs and symptoms of psychopathology.